Henning Berg was sacked as manager on Thursday following one win in 10 games at the helm.
Rovers' senior coaching staff were also shown the door and, under the caretaker control of reserve-team boss Gary Bowyer, it was the only signing of Berg's 57-day reign that opened the scoring at Oakwell.
On-loan Manchester United forward Josh King's bundled home before the half hour and a sublime individual effort on the stroke of half-time from Ruben Rochina gave Blackburn breathing space.
Stephen Dawson reduced the arrears during a lacklustre second half, the closing stages of which were marred by the sight of Barnsley forward Marcus Tudgay receiving lengthy treatment following a collision with Rovers goalkeeper Jake Kean and leaving the field on a stretcher.
That reduced Keith Hill's side to 10 men having used all their substitutions and, in the eighth of nine additional minutes, Jordan Rhodes muscled his way on to Jason Lowe's long ball to seal Blackburn's triumph and send Barnsley to the foot of the table.